1. Technical Field
The present disclosure relates to an image forming apparatus, such as a copier, a facsimile machine, and a printer, provided with a fixing unit that, by heating and fusing an unfixed toner image carried on a recording medium, fixes the image onto the recording medium, and, in particular, to a mechanism for processing a paper jam occurring between the fixing unit and a discharge unit located above the fixing unit.
2. Description of Related Art
Known as a fixing unit mounted in a conventional image forming apparatus using an electrophotographic method are: a heat roller fixing system in which at least one roller of a fixing roller pair forming a nip has a heat source built therein to thereby serve as a heating roller, and paper which carries an unfixed toner image is passed through the nip portion of this roller pair, so that the toner is fixed onto the paper; and a belt fixing system in which instead of the heating roller a heating belt is used which absorbs radiant light from a heat-generating source emits heat. The paper having the toner image fixed thereonto by the fixing unit is discharged onto a discharge tray by a discharge roller pair disposed on the downstream side of the fixing unit in a paper conveyance direction.
In a known configuration for an image forming apparatus provided with such a fixing unit, the paper conveyance path from the nip portion of the fixing roller pair to the discharge roller pair is designed to be openable in order to facilitate processing of a paper jam occurring around the fixing unit. For example, an image forming apparatus is known which has a fixing device provided with an openable first cover (detachment member protection cover) covering a separating member for separating paper from a heat fixing roller and an openable second cover (fixing jam processing cover) covering the first cover.
In the aforementioned image forming apparatus, if a jam occurs somewhere between the nip portion of the fixing roller pair and a conveyance guide member, jam processing can be safely performed by opening only the second cover, with the separating member, which is hot, covered by the first cover. On the other hand, if a jam occurs such that an edge of the paper is caught between the separating member and the fixing roller or such that the paper is completely wound around the fixing roller, jam processing can be performed by opening the first and second covers.
From another viewpoint, to minimize the height of an image forming apparatus, it helps to adopt a configuration in which the conveyance guide member is provided in an upper end portion of the fixing jam processing cover so that paper is guided to a paper discharge path closely above the fixing unit. However, in this configuration, in order to guide paper to the discharge roller pair disposed obliquely above the fixing device, the conveyance guide member is disposed obliquely upward. As a result, when the fixing jam processing cover is opened and closed in a vertical direction with a lower end portion thereof as a pivot, inconveniently, the conveyance guide member interferes with an upper portion of a main body of the image forming apparatus, hence hindering smooth opening and closing of the fixing jam processing cover. Incidentally, in the configuration of the previously mentioned image forming apparatus, the conveyance guide member is not provided in an upper end portion of the fixing jam processing cover, and therefore upon opening and closing the cover, the conveyance guide member does not interfere with the main body of the image forming apparatus.
One possible way to avoid interference of the conveyance guide member with the upper portion of the main body of the image forming apparatus upon opening and closing the fixing jam processing cover is to place a part of the apparatus main body frame of the image forming apparatus which may interfere with the conveyance guide member clear of the cover opening and closing trajectory. This, however, accordingly increases the height of the image forming apparatus. An attempt to avoid interference with the conveyance guide member may also be made by forming a cut or an opening in a part of the apparatus main body frame. This, however, reduces the stiffness of the apparatus main body of the image forming apparatus. In particular, in a case where an image reading unit is mounted above an upper part of the apparatus main body as in an MFP (multi-functional peripheral), and accordingly a reinforcement member such as a metal sheet is indispensable closely above the fixing unit, the method being discussed, in the first place, does not permit a reinforcement member to be provided in the opening and closing trajectory of the conveyance guide member, possibly leading to insufficient stiffness of the apparatus main body.